Method of drying



Patented Sept. 27, 1938 UNITED STATES PATENT OFFICE E. Garono, Buffalo,N. Corporation, New York, N. Y.,

New York Y., assignors to Research a corporation of No Drawing.Application August 26, 1935, Serial No. 37,936

'1 Claims.

This invention relates to the drying of wet porous insoluble solids andparticularly of those which contain non-volatile solutes which, inlocalized high concentration, are undesirable,

When porous materials dry, solutes are carried by the solvent along thecapillary channels in the mass and congregate near the surface inincreasing concentrations. Although the original concentration ofsolutes may be so low as to have no harmful effect, yet the highconcentration built up in the surface layer frequently is destructive.

If the tanning of leather be taken by way of example, the tanned hide isuniformly saturated with tanning liquor and then dried. As waterevaporates from the surface, the tanning substances, whether they betrue solutes or colloidal particles, are carried by the liquor throughthe capillary channels between the hide fibers until the surface isreached. There they remain while the water evaporates. If the drying ofa hide is carried on much above 80 to 90 F. the surface is discoloredand badly scorched. This condition is evidenced by discoloration and bybrittleness. Deep cracks form whenever the leather is flexed.

We have discovered that one may prevent all harmful concentration ofdissolved substances at the surface and consequently, may dry suchsubstances as leather at high temperatures and at higher evaporationrates than heretofore has been possible.

The objects of our invention, therefore, are to avoid the concentrationof deleterious substances adjacent the surface of a drying mass; toavoid harmful concentrations of tanning substances at the surface of theleather; to secure a more uniform distribution of the substances withinthe dried hide; to dry at temperatures and at rates which heretoforehave been destructive; to secure good color without the necessity of ableaching operation; and generally, to secure more uniform distributionof dried solutes in a dried-out mass. These and other objects willbecome apparent from the specification. h

According to our invention, and again taking leather as an example, wecoat the wet hide with a porous mass possessing a multiplicity ofcapillary channels and through these channels and from the temporary,removable surface so pro- 5 duced, evaporate the water. The tanningsubstances contained in the wet leather, instead of concentrating at theleather-air interface as previously, cross the boundary of the leather,

enter the porous mass and now concentrate at 55 the new air-porous massinterface.

Thus, there is no high concentration of tanning substances anywhere inthe hide and, consequently, it may be dried at a temperature as high as180 F. with no discoloration or embrittlement of the surface. Unbleachedleather 5 when dried by the same method is practically identical inapearance to leather which previously has been bleached.

A great variety of coating materials are suitable since it is onlynecessary that they be capill0 lary active substances and form a coatthick enough to hold the whole layer of concentrated tanning agents. Acoating of plaster of Paris may be cast against the leather, or a clayslip poured thereover, or a sheet of fibrous material such as a paperfelt or even newspaper stock (for thinner leathers) may be rolled intocontact with the hide, but we have found coatings of finely dividedmineral substances are the cheapest and the easiest both to apply and to20 remove. We prefer to daub a thick slurry of kieselguhr over theliquor-soaked hide. Fine sand, slate flour, fullers earth and otherclays may be used in place of kieselguhr with practically equal effect.

Although we prefer such inorganic coatings, organic coatings are alsosuitable, cotton flock, wood flour held in starch or flour paste or evenstarch or flour pastes alone form satisfactory absorptive coatings.

Essentially, therefore, our invention may be practiced by applying atemporary coat of a capillary active substance to the material to bedried and allowing the deleterious substances to con centrate thereinthroughout the drying process. 35 When the drying is complete thecapillary active substance is stripped or dusted off from the driedmaterial.

Many of the coating substances, but particularly kieselguhr, may berecovered for reuse by 40 dumping whatever material is dusted off fromthe dried hide into water and allowing the tanning substances to leachout. When the sludge has settled, the water plus the tannin may be runoff. The sludge is then mixed with fresh water to 45 give it the properconsistency for reuse.

As a specific example of our invention, 85 parts of kieselguhr and 15parts of fine sand are mixed with a sufficient amount of water to forma. stiff paste. This is painted over the wet hide. The hide isimmediately placed in a drying shed and the temperature maintained atabout 180 F. The time required for drying is, of course, dependent uponthe water content, the thickness of the hide, and the humidity in theshed and,

consequently, we give no time therefor, but it has been our experiencethat large, thick parts may be thoroughly dried in this manner in fromsix to eighteen hours.

According to the statutory requirement, we have set forth the preferredexample of our process as applied to the drying of leather, but weintend no limitation thereby. It is evident that the process isapplicable to the drying of any substance wherein a concentration ofsolutes is undesirable at the surface.

What we claim therefore is:

l. The process of drying wet porous masses having solutes therein whichcomprises covering a surface of the mass with a water slurry of acapillary-active substance which is insoluble in water, therebydepositing a relatively thin adherent coating of said substance on thesurface of said mass. maintaining the substances and the mass in closecontact, and drying both the mass and the substance by evaporation ofwater from the surface of the coating of substance, whereby excesssolutes leave the mass and concentrate in the coating of substance.

2. The process of drying leather which comprises coating the wet hidewith a water slurry of a finely powdered material capable of forming acapillary-active layer, evoporating water from the surface of saidlayer, and thereby causing the excess tanning substances present in thehide to concentrate in said layer and removing the finely powderedmaterial from the hide.

3. The process of drying leather which comprises coating the dryingsurface of a wet hide with a relatively thin layer of a water slurry ofa comminuted material capable of forming a capillary active layer,subjecting the layer to drying conditions and thereby drying the hideand removing the comminuted material from the hide.

4. The process of tanning which comprises submitting the hides to a.tanning bath, coating the wet hides taken from said bath with a waterslurry of finely powdered material capable of forming a capillary-activelayer, evaporating water from the surface of the layer, to thereby causethe excess tanning substances present in the hide to concentrate in thecapillary-active layer, and removing the finely powdered material fromthe hides.

5. The process of drying wet hides containing a tanning solution andpreventing concentration of solutes at the surface of said hides, saidprocess comprising covering the surface of said hides with a waterslurry of a finely powdered material which is insoluble in said tanningsolution, thereby depositing a relatively thin adherent coating of saidsubstance on the surface of said hides which has a capillary actionsufficient to draw the tanning solutes from the surface of said hides,drying said layer by evaporation while allowing the excess tanningsolutes to concentrate in said layer of capillary active material, andremoving said layer from said hides.

6. Process of drying leather as defined in claim 3 in which the finelypowdered material is kieselguhr.

7. Process of drying leather as defined in claim 3 in which the finelypowdered material is fuller's earth.

THOMAS K. SHERWOOD. LOUIS E. GARONO.

CERTIFICATE OF CORRECTION Patent No. 2,131, 614.5.

September 27, 1958.

THOMAS K. SHERWOOD, ET AL.

It is hereby certified that error a ppears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,first column, line 28,

claim 2, for "evoporating' read evaporating; and second column, lines 29and 52, claims 6and7 respectively, for the claim refer ence numeral "3"read 2; and that the said Letters Patent should be read with thiscorrection therein that the samemay conform to the record of the case inthe Patent Office.

Signed and sealed this 1st day of November,

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

consequently, we give no time therefor, but it has been our experiencethat large, thick parts may be thoroughly dried in this manner in fromsix to eighteen hours.

According to the statutory requirement, we have set forth the preferredexample of our process as applied to the drying of leather, but weintend no limitation thereby. It is evident that the process isapplicable to the drying of any substance wherein a concentration ofsolutes is undesirable at the surface.

What we claim therefore is:

l. The process of drying wet porous masses having solutes therein whichcomprises covering a surface of the mass with a water slurry of acapillary-active substance which is insoluble in water, therebydepositing a relatively thin adherent coating of said substance on thesurface of said mass. maintaining the substances and the mass in closecontact, and drying both the mass and the substance by evaporation ofwater from the surface of the coating of substance, whereby excesssolutes leave the mass and concentrate in the coating of substance.

2. The process of drying leather which comprises coating the wet hidewith a water slurry of a finely powdered material capable of forming acapillary-active layer, evoporating water from the surface of saidlayer, and thereby causing the excess tanning substances present in thehide to concentrate in said layer and removing the finely powderedmaterial from the hide.

3. The process of drying leather which comprises coating the dryingsurface of a wet hide with a relatively thin layer of a water slurry ofa comminuted material capable of forming a capillary active layer,subjecting the layer to drying conditions and thereby drying the hideand removing the comminuted material from the hide.

4. The process of tanning which comprises submitting the hides to a.tanning bath, coating the wet hides taken from said bath with a waterslurry of finely powdered material capable of forming a capillary-activelayer, evaporating water from the surface of the layer, to thereby causethe excess tanning substances present in the hide to concentrate in thecapillary-active layer, and removing the finely powdered material fromthe hides.

5. The process of drying wet hides containing a tanning solution andpreventing concentration of solutes at the surface of said hides, saidprocess comprising covering the surface of said hides with a waterslurry of a finely powdered material which is insoluble in said tanningsolution, thereby depositing a relatively thin adherent coating of saidsubstance on the surface of said hides which has a capillary actionsufficient to draw the tanning solutes from the surface of said hides,drying said layer by evaporation while allowing the excess tanningsolutes to concentrate in said layer of capillary active material, andremoving said layer from said hides.

6. Process of drying leather as defined in claim 3 in which the finelypowdered material is kieselguhr.

7. Process of drying leather as defined in claim 3 in which the finelypowdered material is fuller's earth.

THOMAS K. SHERWOOD. LOUIS E. GARONO.

CERTIFICATE OF CORRECTION Patent No. 2,131, 614.5.

September 27, 1958.

THOMAS K. SHERWOOD, ET AL.

It is hereby certified that error a ppears in the printed specificationof the above numbered patent requiring correction as follows: Page 2,first column, line 28,

claim 2, for "evoporating' read evaporating; and second column, lines 29and 52, claims 6and7 respectively, for the claim refer ence numeral "3"read 2; and that the said Letters Patent should be read with thiscorrection therein that the samemay conform to the record of the case inthe Patent Office.

Signed and sealed this 1st day of November,

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

